Because of their ease of handling, heat resistance, adherence and good electrical properties, room temperature vulcanizable (RTV) silicone rubber compositions which crosslink with moisture are used in a wide variety of applications including building sealants and adhesives for electrical and electronic parts. In the applications of electrical and electronic parts, especially sealing of microwave oven window frames, silicone rubber which crosslinks with moisture is often employed due to heat resistance and adherence. In the window frame sealing application, the silicone rubber as cured is required to have initial adherence and heat resistant adherence to the adherends, glass and coated steel plate and to maintain adherence even upon exposure to hot steam. To impart tack to RTV silicone rubber, the addition of silane coupling agents in the form of silicon compounds is effective. However, RTV silicone rubber compositions containing various conventional silane coupling agents such as minopropyltriethoxysilane are good in initial adherence and heat resistant adherence, but fail to improve adherence upon exposure to hot steam.
For example, U.S. Pat. No. 4,629,775 and JP-A 61-64753 disclose RTV silicone rubber compositions comprising as adhesive aids the reaction product of a mercaptosilane with an isocyanate or polyisocyanate compound. They are good in initial adherence, but insufficient in adherence upon exposure to hot steam.